This invention relates to an outboard motor and more particularly to an improved crankcase ventilation arrangement for an outboard motor utilizing a small four cycle engine.
Four-cycle engines are being considered seriously as replacements for the more conventionally utilized two-cycle engines as power plants in outboard motors. Although the two-cycle engine has an advantage in providing a less complicated, higher specific output structure than a four-cycle engine, there are some environmental concerns with the ability to adequately control the exhaust emission from two-cycle engines. Therefore, four-cycle engines are being considered to replace two-cycle engines in this application.
There are some specific problems in connection with the use of four-cycle engines in outboard motors that are unique to this specific application. One of these has to do with the orientation of the engine in the power head. In most conventional applications for four-cycle engines, the crankcase chamber is positioned at the lower end of the engine and the cylinders extend generally vertically upwardly from the crankcase chamber. With an outboard motor application, however, the engine is generally mounted so that the crankshaft rotates about a vertically extending axis. This is done to facilitate connection of the crankshaft to the drive shaft which drives the propulsion unit in the lower unit portion of the outboard motor.
In order to achieve higher specific outputs for four-cycle engines to make them more feasible to replace two-cycle engines, such arrangements as overhead valves and overhead cam shafts are frequently employed. This raises additional problems due to the vertical disposition of the crankshaft.
For example, it is generally the practice to vent blow-by gases from the engine crankcase chamber to the engine induction system so as to avoid emission of hydrocarbons to the atmosphere. By so recirculating the blow-by gases back to the combustion chamber, any hydrocarbons can be burned and oxidized so as to reduce unwanted hydrocarbon emissions. A wide variety of types of crankcase ventilating systems are employed for this purpose.
These systems generally, however, rely on the vertical disposition of the cylinder bore with the valve chamber above the crankcase chamber for their effective operation.
Where the engine is disposed horizontally, different types of ventilation systems are required.
It is, therefore, a principal object of this invention to provide an improved crankcase ventilation and blow-by system for a four-cycle outboard motor.
It is a further object of this invention to provide an improved and simplified four-cycle crankcase ventilating system that facilitates utilization with outboard motors.
Although the return of the blow-by gases and crankcase ventilating gases to the combustion chamber for combustion is useful in reducing hydrocarbon emissions, there is a risk that because of the horizontal disposition of the cylinder that oil may also be drawn through this ventilating system and delivered to the combustion chamber. This can give rise to undesirable exhaust gas constituents and also can cause the oil consumption of the engine to become unacceptably high.
It is, therefore, a still further object of this invention to provide an improved crankcase ventilating system and oil separator arrangement for use in four-cycle outboard motors.